Stock Incentive Plans - Employee Stock Purchase Plan (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jun. 21, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)	30,928,290		25,157,139
Stock-based compensation expense	$ 1,780	$ 1,409
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized and reserved for future issuance (in shares)	2,546,464			173,076
Number of shares authorized, increase (in shares)	1,080,711	863,254
Shares of common stock issued to employees under the ESPP (in shares)	34,696
Stock-based compensation expense	$ 100	$ 100